1. Technical Field
The present invention—involving bookbinding apparatuses that collate sheets onto which images have been formed in an image-forming or like apparatus, and that bind them into books by applying adhesive to the spine part of blocks of the sheets and binding them together with a cover sheet—relates to casing-in bookbinding apparatuses that join sheet blocks, onto the spine part of which glue has been applied, to the middle portion of a cover sheet, and spine-crease the cover sheet.
2. Description of the Related Art
Generally, this kind of bookbinding apparatus is used as a terminal device to an image forming apparatus, such as a printer, printing press, or the like. Widely used among such apparatuses are automated bookbinding systems that stack image-bearing sheets in page order to collate them into blocks, then apply glue to an endface of a block and encase it with cover sheet. Also in wide use are bookbinding apparatuses that collate into sets printed sheets delivered from a discharge outlet, then encase the sets in cover sheets. A variety of systems have been proposed that print documents, and at the same time execute the bookbinding process that automatically binds and covers the documents to form a booklet. A recent particular example is on-demand printing systems, known in electronic publishing.
As an example of such a system, Japanese Unexamined Pat. App. No. 2004-209869 discloses an apparatus configuration that automatically finishes booklets of sheets received from an image forming apparatus. This patent publication also discloses an adhesive application process wherein sheets received from an image forming apparatus discharge outlet are guided to a sheet conveyance path, and stacked substantially horizontally at a stacking tray disposed downstream in that path. The horizontally stacked sheet bundle is rotated substantially 90 degrees to be guided to an adhesive applicator apparatus. An apparatus that folds a cover sheet supplied from an inserter over a sheet bundle applied with adhesive is also disclosed.
Bookbinding schemes such as the conventional bookbinding system are known to join the glued spine part of a sheet bundle to a center of a cover sheet conveyed orthogonally to the direction of sheet bundle conveyance and fold the cover sheet over the sheet bundle, thereby forming a booklet. In conventional apparatuses, a pair of spine-creasing press members (disposed at left and right sides of a creasing position) presses the cover sheet joined at its center to the sheet bundle. Therefore, a structure is adopted wherein the pair of spine-creasing press members forms a pressing shape. The pressing members mutually approach each other from their standby positions, separated a distance at left and right sides based on a central spine-creasing position, to fold the spine part of the cover sheet at the central spine-creasing position.
Thus, when the cover sheet is folded over the glued sheet bundle, the sheet bundle and cover sheet spine part are press-formed by the pair of spine-creasing press members. In this case, the left and right of the pair of press members are positioned at their standby positions, such as their home positions. They press-form the spine part of the cover sheet over the sheet bundle when they move from the standby positions to a creasing position (or spine-creasing position). Therefore, there are problems, outlined below, caused by differences in sheet bundle thickness. Firstly, if the left- and right-side spine-creasing press members do not reach and press against the spine part of the sheet bundle at the same time, the sheet bundle can be pushed out of position. That invites unsightly damage to the finished booklet. Secondly, if it takes a long time for the left- and right-side spine-creasing press members to reach the spine part of the sheet bundle from their standby positions, there is the possibility that the adhesive will harden or solidify, depending on the ambient temperature. If that should occur, the cover sheet will not fold properly over the spine part of the sheet bundle. This situation leads to unevenness or even wrinkles in the finished booklet.
Conversely, if the press members move too quickly to fold the cover sheet over the spine part of the sheet bundle, there is the problem that the softened adhesive will bleed through the cover sheet and ruin the finished booklet. Adhesive used when binding a booklet requires certain contradictory conditions for an optimum finished product. Specifically, adhesive must be adequately viscid to be able to permeate between the leaves of the sheet bundle, yet it must attain a proper degree of hardness when the cover sheet is folded over the sheet bundle for a clean fold. Furthermore, once the cover sheet has been folded, the adhesive must solidify in a short amount of time.
On the other hand, sheet bundles will vary in thickness, so the conditions for folding a cover sheet over a thick or a thin bundle will also vary. Conventional left- and right-side spine-creasing press members approach each other from predetermined standby positions at a predetermined speed, and fold the cover sheet at a predetermined creasing position. Therefore, if the thicknesses of sheet bundles are different, the timing for those left- and right-side spine-creasing press members to reach the creasing position will also vary accordingly. This can lead to the spine-creasing position varying to the left or right sides, and again produce an improperly folded booklet. Even if the problem of mis-positioning is overcome, the spine-creasing press members reach a thick sheet bundle more quickly from their standby positions, and take a longer amount of time for thinner sheet bundles. Thus, the degree of adhesive solidification at the time of the cover sheet folding operation varies depending on the thickness of the sheet bundle.
Conventionally, to solve the aforementioned problems, various measures have been attempted, such as using a slower drying/hardening adhesive or standing by until the adhesive has reached a sufficient degree of hardness before folding the cover sheet. However, these measures result in extended production times to finish booklets. Thus, an object of the present invention is to provide a bookbinding apparatus that accurately folds a cover sheet over a sheet bundle regardless of the sheet bundle thickness, and completes the bookbinding process in a short amount of time without negatively affecting the aesthetic appearance of the finished booklet after the bookbinding process.